Typically a disk drive is used to store data. The disk drive can be, among other things, a direct access storage device (DASD) or a hard disk drive (HDD) and can include one or more disks and a disk controller to manage operations on the disks. The disks can be stacked vertically on a spindle by placing the spindle in the center of the disks. The spindle can be turned by a motor at velocities ranging from three to fifteen thousand revolutions per minute. The part of the disk that is nearest the spindle is commonly referred to as the inner diameter (ID) and the part of the disk that is furthest from the spindle is commonly referred to as the outer diameter (OD).
A read write head can be used to write data to and read data from a disk. The read write head is associated with a slider. The slider provides mechanical support for the read write head and electrical connections between the head and the drive. The slider can be attached to a suspension to form a head gimbal assembly (HGA). The HGA can be attached to an actuator arm, which is a part of an actuator assembly, to move and support the HGA. Further the slider includes a pattern of shaped pads on the air bearing surface (ABS) of the slider, which enables the slider to “fly” on an air cushion at a desired height above a disk.
The fly heights of a population of sliders can be plotted as depicted in FIG. 1. The vertical axis represents the frequency and the horizontal one the fly height. The standard deviation a (also known as “fly height sigma”) of the population can be used to measure the fly height spread of a group of parts sharing the same air bearing design. For example, σ1 indicates that the fly heights of this population are more spread apart than another population with σ2.
Manufacturers attempt as much as possible to create sliders that have approximately the same fly heights. The more similar the fly heights for a population of sliders are, the easier it is to manufacture disk drives that operate in a predictable manner and the fewer sliders that the manufacturer will have to dispose of. Therefore, manufacturers of sliders are constantly looking for ways to design sliders that provide as small of a fly height sigma as possible since this will enable them to manufacture disk drives more quickly, that are of superior quality and at a reduced cost.